Thyroid hormone therapy provides the body with manufactured hormones when the thyroid gland cannot produce enough on its own. This treatment, taken in pill form, restores normal metabolic function by replicating the body’s natural hormone levels. The purpose is to ensure all cells receive the necessary signals to function correctly. By replacing missing hormones, the therapy helps maintain energy use, temperature regulation, and the function of the brain, heart, and muscles.
Conditions Requiring Thyroid Hormone Therapy
The most frequent reason for thyroid hormone therapy is hypothyroidism, where an underactive thyroid fails to produce adequate hormone levels and slows the body’s metabolism. A common cause is Hashimoto’s disease, an autoimmune disorder in which the body’s immune system attacks the thyroid gland. This gradually diminishes its ability to produce hormones.
Thyroid hormone replacement is also necessary after certain medical procedures. Individuals who have undergone a thyroidectomy (surgical removal of the thyroid) require lifelong therapy. This procedure is performed to treat thyroid cancer or large goiters. Therapy is also required following radioactive iodine (RAI) treatment, which is used to destroy thyroid tissue. In these instances, the therapy can also help suppress the regrowth of cancerous tissue.
Types of Thyroid Medications
The most common medication is Levothyroxine, a synthetic version of the thyroxine (T4) hormone. It is the standard of care because the body converts T4 into triiodothyronine (T3), the active hormone used by cells. This conversion process allows the body to regulate active hormone levels, mimicking a healthy thyroid. Levothyroxine provides a steady supply of T4, making it the preferred initial treatment.
Another medication is Liothyronine, a synthetic form of the T3 hormone. Because T3 is the active hormone, Liothyronine has a more rapid onset and shorter duration of action. It is less commonly used as a standalone treatment because it can cause peaks and troughs in T3 levels, which may lead to side effects. For some individuals who do not convert T4 to T3 efficiently, combination therapy with Levothyroxine might be beneficial.
Desiccated Thyroid Extract (DTE) is derived from the dried thyroid glands of pigs and contains both T4 and T3. Some patients report feeling better on DTE, possibly due to the presence of both hormones. However, the ratio of T4 to T3 differs from that in humans, and the hormone content can be less consistent than synthetic medications, making dosage regulation more challenging.
Potential Side Effects
Side effects from thyroid hormone therapy are nearly always a result of an incorrect dosage, not a reaction to the medication itself. When the dose is properly calibrated, most people experience no side effects. Any adverse symptoms indicate that this balance has not been achieved and are reversible once the dosage is adjusted.
If the dose is too high, it can mimic hyperthyroidism by overstimulating the body’s metabolism. Symptoms of overmedication include feeling anxious, irritable, or shaky. A person might also experience insomnia, heart palpitations, an intolerance to heat with excessive sweating, and unexplained weight loss.
Conversely, a dose that is too low will not fully alleviate the symptoms of hypothyroidism. A person on an insufficient dose will continue to experience signs of an underactive thyroid. These can include persistent fatigue, unexplained weight gain, a heightened sensitivity to cold, constipation, and dry skin and hair.
Treatment Monitoring and Dose Adjustment
Managing thyroid hormone therapy relies on regular monitoring with blood tests. The primary test used is the Thyroid-Stimulating Hormone (TSH) test. A high TSH level suggests the medication dose may be too low, while a very low TSH level can indicate the dose is too high. Doctors may also measure Free T4 levels to assess the amount of available thyroid hormone.
When treatment begins, a doctor calculates an initial dose based on the patient’s weight, age, and the severity of their hypothyroidism. After starting the medication, blood tests are repeated in six to eight weeks to evaluate the body’s response. Based on these TSH and Free T4 results, the physician will make precise adjustments to the dosage.
Effective treatment requires consistency. Thyroid medication should be taken at the same time each day, on an empty stomach 30 to 60 minutes before the first meal, to ensure consistent absorption. Certain supplements, like calcium or iron, can interfere with its absorption and should be taken several hours apart. Because hormone needs can change over time due to aging or weight changes, lifelong monitoring with regular check-ups is a standard part of the therapy.